Philippe V, the King of Spain (Mark Rylance), is not ill but indisposed.  He’s talking to goldfish, obsessing over clocks, and occasionally lapsing into violence.  The vultures are circling, while his second wife, Isabella (Melody Grove), provides a buffer between Philippe and his slavering council.  Sometimes, Philippe appears lucid, offering aphorisms that suggest he is aware of the chaos he creates.  “Many gods are fun,” he muses while his court descends into disarray, “one is a nightmare.”

Enter Farinelli (Sam Crane), a castrato whose ethereal voice banishes all the others, imagined and real.  For a time, the King recovers his agency if not his sanity, leading Isabella and Farinelli on a quixotic journey into the woods to “hear” the stars.  In this edenic space, they cook for themselves and listen to the vibrations of the planets, “the music of the spheres” in Philippe’s lyrical wording.

Claire van Kampen’s Farinelli and the King, inspired by the now scientifically-vindicated neurological benefits of music, is a sweet little bedtime story.  The play unapologetically sides with fantasy over reality, with the fancies of a Spanish king over the hard-nosed realism of his inner circle.  Whenever Farinelli sings, Mr. Crane is joined onstage by the countertenor Iestyn Davies; his voice, combined with the uncanny twinning of the characters, provides a nice fairy tale effect.  And he does, indeed, sound like the music of the stars.

Mr. Rylance, of course, is probably our greatest living stage actor, and his presence is enough to make even the lousiest play required viewing.  Farinelli isn’t perfect: it loses focus in the second act, and apart from her enamored endorsement of a Peter Pan-like refusal to face the grime of ordinary life, I’m not quite sure Ms. Van Kampen knows exactly what this material means to her.  The introduction late the in play of romantic feelings between Isabella and Farinelli, for example, is both undercooked and distracting.  Still, Farinelli abounds in charm, and I don’t think I’ve ever seen Mr. Rylance have so much laid-back fun.  I don’t believe in kings—or in gods, for that matter—but he may be the closest we have to either.

Farinelli and the King runs through March 25th at the Belasco Theatre.  111 W. 44th Street  New York, NY.  2 hours 30 minutes.  One intermission.